1. Field of the Invention
The present invention relates to LED (light emitting diode) lighting circuit, and more specifically to a control circuit and a control method for dimming LED lighting circuit.
2. Description of the Related Art
FIG. 1 shows a dimmable lighting circuit 100 in conventional arts. The dimmable lighting circuit 100 basically comprises a bilateral triode thyristor TRIAC 110, a bridge rectifier 120 and a load 130. The TRIAC 110 receives an alternating current (AC) mains VAC. By controlling a gate voltage of the TRIAC 110, a power sourced from the AC mains VAC can be delivered to the load 130, such as an electric bulb, through the bridge rectifier 120 to achieve dimmable lighting control.
However, in order to make the state of TRIAC 110 being kept at the turning-on state, a minimum holding current is required. That is, a current IAC flowing through the TRIAC 110 should be kept higher than the minimum holding current of the TRIAC 110. However, the level of the load current ILD supplied to the load 130 is equal to that of the current IAC. Therefore, the load current LLD needs to meet the requirement of the minimum holding current of the TRIAC 110. Otherwise, if the load 130 is an electric bulb, the TRIAC 110 will be at unstable state between on and off resulting in flickering to the lighting.